The chapter explores in detail the three aspects of aircraft configuration and sizing: aerodynamic, internal, and structural configuration and sizing. From the chapter, the reader will learn how to reduce the trim penalties, what the idea behind area rule is, as well as how the local aerodynamics of an aircraft can be enhanced. The chapter explains what parameters are used to estimate the lateral static stability of an aircraft and how the aircraft geometry can be adjucted to ensure the required level of static lateral stability. This chapter describes some methods for laying out the components of an aircraft and estimating its center of gravity, as well as the center of gravity envelope. The concept of the mean aerodynamic chord is introduced and explained. The chapter offers an algorithm for calculating the center of gravity for an aircraft and provides a sample weight report. The chapter also presents some approaches to ensuring the design center of gravity envelope by design methods. In addition, the chapter discusses special design layouts, such as aft-podded engines, as well as the design of cockpits and passenger cabins. Finally, some guidelines for aircraft structural design are presented.